pm why

Explain why a package is installed

Overview

The pm why command shows why a package is installed in your project by displaying the dependency chain that requires it.

Syntax

pm why <package> [...args]

Arguments

package string required

The package name to investigate

args string[]

Additional arguments passed to the underlying package manager

Examples

Check Why Package is Installed

pm why lodash

Running: pnpm why lodash

dependencies:
lodash 4.17.21
├── my-app
└─┬ some-library
  └── lodash@^4.17.0

Check Transitive Dependency

pm why typescript

Running: pnpm why typescript

devDependencies:
typescript 5.0.0
├── my-app
├─┬ @typescript-eslint/parser
│ └── typescript@>=4.2.0
└─┬ vite
  └── typescript@^5.0.0

Check Deep Dependency

pm why react

Running: pnpm why react

dependencies:
react 18.2.0
├── my-app
├── react-dom → react@^18.2.0
└─┬ @radix-ui/react-dialog
  └── react@^16.8 || ^17.0 || ^18.0

Use Cases

Debug Unexpected Package

Find out why an unexpected package is installed:

pm why some-random-package

Understand Duplicates

Check why multiple versions exist:

pm why react
# Shows all dependency paths requiring react

Audit Dependencies

Investigate security vulnerabilities:

pm why vulnerable-package
# Shows which packages depend on it

Plan Upgrades

Understand dependencies before upgrading:

pm why typescript
# Check what requires specific version

How It Works

From src/commands/why.ts:10-22:

export const whyCmd = cli.Command.make('why', { args: argsArg }, (args) =>
  Effect.gen(function* () {
    const pm = yield* PackageManagerService;
    if (pm.name === 'npm') {
      yield* Console.error('why is not supported for npm');
      return;
    }
    const passthrough = Array.from(args.args);
    const cmd = ShellCommand.make(pm.name, 'why', ...passthrough);
    yield* Console.log(`Running: ${pm.name} why ${passthrough.join(' ')}`);
    yield* runShellCommand(cmd);
  }).pipe(Effect.provide(PackageManagerLayer)),
);

The command:

Detects your package manager
Checks if it’s npm (not supported)
Passes arguments to pnpm why or bun why
Displays the dependency tree

Package Manager Support

Package Manager	Supported	Command
pnpm	✅ Yes	`pnpm why <package>`
bun	✅ Yes	`bun why <package>`
npm	❌ No	Not available

Alternative for npm

If you’re using npm:

npm ls lodash

This shows where the package is used, but with different formatting.

Understanding Output

The output typically shows:

Package version - The installed version
Dependency type - Whether it’s in dependencies, devDependencies, etc.
Dependency chain - The tree of packages that require it
Version ranges - The semver ranges that satisfied the requirement

Example Output Explained

pm why react

dependencies:               # Found in dependencies
react 18.2.0               # Installed version
├── my-app                 # Direct dependency
├── react-dom → react@^18  # Via react-dom (requires ^18)
└─┬ ui-library             # Via ui-library
  └── react@^18.0.0       # Which requires ^18.0.0

This tells you:

React 18.2.0 is installed
It’s a direct dependency of your app
react-dom requires react ^18
ui-library also requires react ^18.0.0

Common Scenarios

Find Dependency Source

pm why @types/node
# Shows which packages need Node.js types

Debug Version Conflicts

pm why react
# If multiple versions exist, shows all paths

Identify Bloat

pm why large-package
# Check if it's really needed

Security Audit

pm why vulnerable-package
# Find all dependents before removing

Workflow Examples

Remove Unused Dependency

Check Usage

pm why lodash

If No Direct Use

If it’s only a transitive dependency, consider alternatives

If Direct Dependency

Remove safely:

pm remove lodash

Investigate Duplicate

Check Why Installed

pm why react

Review Version Ranges

Check if dependencies can use the same version

Update Dependencies

Align versions to remove duplicates:

pm up react

pm ls - List installed dependencies
pm remove - Remove dependencies
pm up - Update dependencies